Two new melanodrymiid snails from the East Pacific Rise indicate the potential role of inactive vents as evolutionary stepping-stones

Abstract

Since their discovery in 1977, animals specialized to life in active deep-sea hydrothermal vents have been the focus of many studies. Inactive spires in the vent periphery, however, have received little attention. Recent shifts of deep-sea mining interests from active vents to inactive sulphide deposits have led to an urgent need to characterize the inactive vent fauna. Here, we report two new species of the vent-endemic genus Melanodrymia that are apparently specific to surfaces of inactive sulphides on the East Pacific Rise. Melanodrymia laurelin sp. nov. and M. telperion sp. nov. are easily distinguished from other congeners by shell shape and sculpture; their standings as distinct species are supported by molecular analyses using the mitochondrial cytochrome c oxidase subunit I (COI) gene. They were collected together with numerous specimens of M. galeronae, another species originally described some distance away from active vents. Phylogenetic reconstruction indicates Melanodrymia species living in active vents likely evolved from ancestors specializing in inactive spires, and in turn from sunken wood. Our findings add to the growing evidence that inactive sulphides host unique species, bolstering the need to better understand these systems before any anthropogenic exploitation takes place. https://zoobank.org/urn:lsid:zoobank.org:pub:D8E8EB3F-B246-4962-B70C-1CD94AEB134D